. . . "appending two data sets together and performing a least square regression fit for an assumed model form using the logarithm of observed sales data and markdown data, wherein if the data sets have n entries each, then the model being fitted in the log space is lnY=lnA+??m+??+ln??, where Y is a vector of size 2n, A is a matrix of [a1 a2], where a1 is a base sale for data set 1 and a2 is a base sale" .